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A Hubble Space Telescope color image of a small portion of the cluster only 0.63 light-years across reveals eight white dwarf stars (inside blue circles) among the cluster's much brighter population of yellow sun-like stars and cooler red dwarf stars.

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A white dwarf is the last stage in the life cycle of a star like the Sun, after it has contracted to a diameter smaller than that of Earth. Incredibly dense, one teaspoon of white dwarf material would weigh about five tonnes.

Nathan Dickinson, a postgraduate student in the University's Department of Physics and Astronomy, is researching the chemical composition of white dwarfs for his PhD. He is particularly interested in the presence of 'heavy elements' in and around white dwarfs, which are otherwise mainly composed of the two simplest elements, hydrogen and helium.

Data from the Hubble Space Telescope provides a spectrum for each star which reveals its chemical make-up. Older, cooler white dwarfs, with a temperature of less than 25,000 degrees, sometimes contain elements such as oxygen, nitrogen, silicon and iron which have been 'hoovered up' from the remains of planets.

Younger, hotter white dwarfs, above that temperature always show heavy chemicals due to their high temperature. However, they sometimes exhibit more of this material than is expected, which raises the question of whether this extra material also came from planets or whether it originated elsewhere, perhaps in clouds around the star."

"Understanding whether the extra material in hot white dwarfs comes from torn up planets is important," emphasizes Dickinson. "It can give us an idea of how these ancient planetary systems evolve as the star ages, so we get a fuller picture of how solar systems die.

"Being the end point of the life cycles of most stars, white dwarfs are among the oldest objects in the galaxy, so they can tell us about what were in the oldest solar systems. Given that the Sun will end its life as a white dwarf, this could tell us what could ultimately happen to our solar system."

In 2010 Dickinson presented some of his work at the 17th European White Dwarf Workshop in Germany, which has since been published in the journal AIP Conference Proceedings.

"Working at the forefront of this scientific area is extremely exciting," says Dickinson. "I find being one of a relatively small community of people in the world to work on this particular area amazing. This work is helping to shape our understanding of how most stars end their lives, how solar systems die, how the environment around these ancient stars behaves and what will ultimately happen to the vast majority of stars in the galaxy.

Pro Vice Chancellor and Head of the College of Science and Engineering, Professor Martin Barstow added: "These are important results which show how younger scientists can be involved in cutting edge research and help the University make important contributions to answering some of the most challenging questions about the Universe and our place within it."

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